ATHOL — The people injured in multi-family apartment building fire at 275 Hapgood St. on Tuesday were one adult, two teenagers and two small children.

Athol Fire Chief John Duguay said the five were transported for smoke inhalation. There was no update on their condition Thursday.

Jennifer Mieth, spokeswoman for the state Department of Fire Services, said the blaze started in a second-floor living room. Duguay said the fire’s cause will likely remain undetermined because the structure had to be demolished so firefighters could get to flames burning in the attic. He also said the building’s wobbly frame was unstable and unsafe.

“The whole front of the building could have fallen down into the street, so we made the decision to take it down,” he said Thursday. All units cleared the scene at 10:28 p.m., he said in a statement.

The fire is under investigation by the office of the State Fire Marshal, the Athol Police Department and the Athol Fire Department.

The four-story building was reduced to a heap of rubble and charred debris as a slight odor of smoke and burned wood lingered in the air Thursday. Yellow caution tape has been used to cordon off the site, which sits on the Hapgood Street’s intersection with Cottage Street.

Neighbor Lorraine Boudreau said she did not know any of the building’s occupants, though people regularly moved in and out.

Mieth said there were rumors that there was a “meth lab” in the basement, but these were unfounded.